This invention relates to tape cassettes, and particularly to means for maintaining tape tension when the cassette is removed from the transport machine.
Tape cassettes usually contain two reels with tape coiled thereon so as to present a free run of tape between the reels, this run being accessible along one side of the cassette that is either open or has a cover door that can be opened when the cassette is inserted into a tape transport machine (e.g., a magnetic tape recording, playing and rewinding machine). Usually also, the sides of the cassette adjacent and orthogonal to the open side have smaller openings for the lateral insertion of a capstan, play-record and erasing heads, and various guides, all of which are part of the transport machine but must engage the tape on the side thereof that faces toward the interior of the cassette. If the free run of tape is too loose, it may drop too far back into the cassette so that the capstan and other such elements fail to pass behind the free tape run and the machine cannot function to transport and record or play the tape; conversely, if the loose run of tape falls too far out of the cassette while it is being loaded, the tape may become tangled in the transport interior mechanism and other malfunctions will result. Also, if the reels are loose when the cassette is being shipped or handled outside the transport machine, then vibrations or other sudden jolts may cause the tape coils to unwind somewhat and sag into conical shapes, resulting in immediate or eventual tape edge damage and later guiding malfunctions in the transport machine.
Previously in the art it has been attempted to control this problem by arranging springloaded friction brakes or pawl-and-pinion combinations within the cassette to lock or restrain the reels in the positions that they occupy at the moment the cassette is withdrawn from the transport machine; and portions of the transport mechanism are arranged to engage the pawls directly or indirectly as the cassette is loaded into the transport to cause the pawls to retract and free the reels while the cassette remains in the machine-loaded condition. Such an arrangement is shown in U.S. Pat. No. 3,900,172, in which the cassette cover door is opened automatically by mechanism within the transport as the cassette is loaded, and the door in turn retracts the pawls that engage pinion gear teeth on the cassette reels.
Such arrangements are limited, however, to perpetuating the tape tension or tape slack conditions that exist at the moment when the cassette is removed from the machine, and the run of tape at the open side of the cassette may still be too loose for proper functioning at the time of the next subsequent insertion. Nothing positive is done to ensure that the tape is actually placed under tension if it is not already in tensioned condition.
Therefore it is an object of the present invention to ensure that the tape is always under tension when the cassette is removed from the transport machine.